Thermally-controlled apparatus



Aug. 18, 1925.

, 1,550,155 A. s. FlTZ GERALD THERMALLY CONTROLLED APPARATUS- Fild May 17, 1923 6 Sheets-Sheet 1 lnVentor'i Alan S..F'it zGe1-a|cl, y M @551 His Attorney.

' Aug. 18,1925. I 1,550,155

A. S. FlTZ GERALD 'THERI'ALLY CONTROLLED APPARATUS Filed May 17 23 e Sheets- Sheet 2 Fig.3..

Inventor Alan S. FTCz Ger-aid, by M w His Attorney.

Aug. 18, 1925. I 1,550,155

A. s. FlTZ GERALD THERMALLY CONTROLLED APPARATUS Filed May 17. 1923 6 Sheets-Sheet 5 Fig.

A. S. FlTZ GERALD THERMALLY CONTROLLED APPARATUS Filed May 17, 923 Y 6 Sheets-Sheet 4 Fig. 6.

- InVentor- Alan S. F'ifz Ger-aid, by M M2,

His Attorney.

Aug. 18,- 1925. 1,550,155

A; S. FITZ ,GERALD THERMALLY CONTROLLED APPARATUS Filed May 17, 1923 6 Sheets-Sheet 5 Inventor Alan 8.7312 Gerald,

His Attorney.

Aug. 18, 1925.

A. s. ,FITZ GERALD THERMALLY CONTROLLED APEARATUS -6 Sheets-Sheet 6 Filed May 17 1923 fngg.

u Q a Y r e l 3 rGfm E w nvu t e C A ./S rm .5 m H N .W

Patented Aug. 18, 1925. v

1,550,155 PATENT OFFICE;

ALAN STEWART FITZGERALD, or LONDON, ENGLAND, ASSIGZNOB 'ro GENERAL ELEC- 'rnrc COMPANY, A CORPORATION on NEW YORK.-

THERMALLY-CONTROLLED APPARATUS.

'Application filed May 17,

To all whom it may concern:

Be it known that I, ALAN STEWART Frrz GERALD, a subject of the British Empire, residing at London, England, have invented certain new and useful Improvements in Thermally-Controlled Apparatus, of which the following is a specification.

This invention relates toelectric thermally controlled apparatus and systems employing the same, 'and particularly to thermal responsiverelays which are intended to function after a predetermined lapse of time.

My invention is applicable to various purposes, but is more particularly intended to provide improved means for operating a relay under conditions involving considerable intervals of time. of the order of minutes rather than seconds.

A further object of the invention is to provide an improved thermal responsive device which may be used'as a time element switch or relay, or may be used for other purposes as well.

j} The design of time lag relays both of the definite time lag and inverse time lag varieties has in the past been commonly carried out on lines involving air or oil dashpots,

v,bellows. or trains of clockwork, having either air vane or eddy-currentescapement. It is found that the designof such relays presents no great difficulty when short time lags of the order of five seconds are required, but that when it is attempted to construct such a relay for delayed action of. considerable duration the rate. of displacement of its moving parts becomes so small that the element of friction is very detrimental to consistent operation, and that unless abnormally heavy actuating forces are employed the relay is liable to give capricious operation and even to fail entirely due to static friction.

In the present invention the use of frictional elements in determining the duration of the time lag is entirely avoided; and in place of such we employ thermo-responsive device caused to be heated from some suitable source, the timel l'ag being arranged to depend upon .both thelrafte of heating as Well "asthe rate of cooling of the" thermo-responsive device. A A In carrying my invention into effect I may employ such devices as compound strip thermostats or the like,-;the preferred'method, however, involving the use of a combined thermal and electrical effect, the ther- 1923. Serial No. 639,626.

mal device consisting of a winding or resistance which is heated from an extraneous source, and the electrical effect consisting of differential or other electrical circuits designed to function "in a suitable manner, and being controlled by changcin resistance of the said winding.

In order to provide a definite time lag thermal responsive relay in accordance with my invention. I arrange to heat the thermal element as readily as possible from some constant supply of energy, and on the same attaining any predetermined.temperature rise, I cause the heating to cease, operation of the relay being arranged to occur when the temperature rise shall have fallen from the above to some lesser-value suitably determined by the required conditions. Compensation for ambient temperature may be made in any desirable manner,'examples being hereinafter described.

The invention is illustrated in the accompanying drawings in which Figures 1' to 9 show, by way of example and diagrammatically, several examples of circuit arrangements for carrying the invention into effect.

For a ready understanding of one of the underlying principles of operation of my invention, reference is first had to the arrangement shown in Fig. 1, in which a relay 1, having a spring controlled armature 9., a. fixed core 3, and two windings 4 and 5,

is employed. The two windings referred to are connected in such away that equivalent currents flowing in the same direction from the source of potential act in opposition.

The windings are connected intwo parallel circuits. in one of which I have a resistance 6, which is constructed of resistance metal of the kind commonly employed in the building of rheostats and is notable for having a low or negligible tempenature coefficient,

while in the other branch of the circuit we connect a resistance 7 constructed of an element having a large positive temperature coefiicient.

The relative resistances of 6 and.

7 "to so arranged that atambient temperawhole circuit be energized from a source of A. C. or D. C. power by the closing of the switch 8, the relay will not immediately operate, but current will flow through .105 equivalent number of turns). If now the.

-6 owing to the resistance of 7 increasing other cases, is shown for convenience of while 6 remains unchanged. It is assumed illustration as operating downwards. Con

excited, but afterwardstwill receive an opv erative excitation varying directly with time relay, is excited across the line in series with branches of the circuit. If the magnitude in series with weather, 12, whi h*1atwr of thiscurrent be so arranged thatappreciresistance is arranged to be short circuit/ed on contact able'heating of bth6 and 7 shall'occur, the by the. armature 13 when resting u as 1n a currentwill diminish in 7, and increase in 14 of a second relay 15, whic in this. case that the supply of energy has tact 14: therefore remains closed .when the constant current characteristics. The .rela relay 15 is deenergized and resistance 12 is therefore, will initially not be operative y thus normally short circuited.

Relay 15, which is purely an auxiliary after the closing of the operating switchB; resistances, 16 and 17:, and is adjusted to )When' suflicient time has elapsed so that the have the following characteristic. If it is' excitation due-to the difference between-the" connected in circuit withlfiand 17 in series,

ampere turns of coils 3 and his of sufiicient it will not operate, but ifoperated by any magnitude, the armature 2' will be attracted means it will under these conditions remain closing the contact 9, and causing terminals closed. If the relay be excited with resist- 10 and 11 to be energized across the source ance 16 short circuited and therefore reoperates in a period of time inversely proportional to the load on the apparatus.

It will be noticed/that the actual durasistance 17 only iii-series, it will operate.

The-relay "15 resets when its coil is deenergized: i is, the armature contact comes to restj on contact 14.

, According to this arrangement I arrange for resistance 16 to be short circuited by the tion of time. for which the relay may be relay 1 when energized to bring the armaset is not definitely limitedby the designer ture on contact 9. It will be seen on referconstruction of the relay, as is the case in ring to the diagram, that no part of the most of the more usual forms of time lag circuit can receive energy until the operat-r relay. By providing particular forms of reing switch 8 is closed. On this being done,

- time lags.

sistance 7 more particularly described hereinafter, a given type of relay may be arranged to'operate with short time legs or long relay 15, this will be" The arrangement described in connected in series with-resistances 16 and Y Fig. 1, however,.has certain definitelimita- 17 and cannot therefore ope-rate". Relay 1, tions, one of which is that it is dependent .however, and its accompanying resistance for its accuracy on its being operated from circuits will be closed across the line, rea constant voltage or. current, and that ersistance 12- being short circuitcd. and under rors will be introduced in accordance with these conditions, it is arranged to take a such variation in the same which may occur. sufiiciently heavy current to cause "heating A further requirement in connection with of the resistance 7'. This latter is designed rot'ective and other forms of definite time for this particular requirement to heat very ag relay is that the relay shallat all times rapidly, and maybe arranged to do this 7 be in a position to provide exactly. the speciwithin a period of the order of 1% of themy present inventioniprovides an arrangelationbetween these two currents, hut-is n tg" mer t in accordagfie with Fig, 2', .in which 'sulficieiitly strong to raise the 7 snn1lar parts indicated with the-same to a temperature very;;much in excess of the; 1

reference mimerals and' certain additional ambient temperature. Directly, therefore,

fied time lag. It will be seen thatthe artotal time lag over which the relay is to rangement above describedwill. only give operate. Immediately following the closthe correct time lag if the actuating impulse iug of switch 8, therefore, 'thereiwill be aoccurswhen resistances 6 and-.7: are both rapid change of resistance and a cor-re at ambient temperatures. Shou1d,'flhowever,- sponding unbalance excitation occurring the relay be energized and deriergized bedue to the windings 4 and 5, which will for]? the completion of the due period, it cause operation of the armature 2. This winot i pulse, as the resistances 6 and 7 will alreaiiy relay 15, whose armature 13, closing, on to ave become heated and therefore will be at the moment when the second 12 to be placed in circuit. Themagnitude' actuating impulse commences. In these cir of'-this resistance 12 is so arranged, that cumstances, therefore, repeated operation when this latter condition obtains. Sam will cause inaccurate operation.

cientfcurrent flows in 6"and 7 to enable thef In ordertoovercome this latter difliculty, relay to function .in accordance with there-f appamtus is shown. j The relay 1 and resisresistance 12 is placed ,in' c mm tanees 6 and 7 arenow connected as she-W 1 'f-commences t0 After due elapse of r ve correct operation it will close contact 9, short circuit -resistanoe immediat y rece ve another acwatmg 1111-116, and cause immediate operation of the.

0t its bottom contact 19, will cause resistanw i ing contact 9.

contact '9 is opened, as this will leave relay energized in series with 16 and 17, under which condition, it has been postulated, the

, relay 15 will retain its armature 13. Therefore, immediately following final 'deencrgization of the relay 1, there will be a complete circuit between the positive source of -power, the terminals 10 and 11, the operating switch 8 and the negative source of Such tripping or other apparatus will be operated; At no previous stage in the sequence of operation can this'complete circuit have been made. Should now an operation occur which is not completed, it will be seen that the error of repeating will be reduced to a minimum as it has'been postulated that the characteristic of the resistance 7 is such that heating occurs very rapidly in comparison withthetime of cooling. On a rapid operation, therefore, such error as may occurwill be confined' to the brief heating period. The cooling curve which determines the whole, with the exception of a small percentage, of the time lag, will remain unaltered at no matter what temperature the resistance 7 may be at the instant when the actuating impulse is received by the operation of switch 8. In the practical application of this'embodiment'of the'invention, switch 8 may be an overload, protective or other form of relay or electroresponsive device. It will be further noted that the terminals Y10 and 11 can only be energized if the switch 8 be held closed for the whole period of" time lag for which the relay is set, and that, as stated in discussing the question of repetition, a repeated operation immediately following will be unaffected by a previous partially completed cycle.

Attention .was drawn above in consideration of Fig. 1 to the fact that a definite time lag can only be obtained by the arrangement of connections shown therein, if the circuit be operated at constant current or constant potential. The same limitation will apply to a less extent to Fig. 2, andwhereas' it may in many cases be'possible to get satisfactory operation where the source of energy is a battery or some other constant supply, it is possible by employing an arrangement as shown in Fig. 3 to compensate for such error as may occur due to variations in the supply line voltage,

Throughout this period, however, armature 13 of relay 15 will havev remained attracted, and contact '19 will have been made. This willstill obtain when In order to achieve this, I provide an ex-,' actly similar circuit with the exception that; I duplicate resistances 6, 7 and 12, and windings 4 and 5. Thus, the resistances 6 and' f are provided for controlling the windings 4' and 5. The one winding 4- is wound in the opposite sense 'to the other winding 4, similarly with the two coils 5 and 5. It is to be noted, however, that only the resistance '12 is cut out by the relay 15. By this arrangement exactly similar operation willbe arrived at to that ob-. tained in Fig; 2, which it will not be necessary to describe again. The characteristics, however, introduced by the additional resistances and windings are such as tov compensate for differences in -the line voltage, and also fordlfi'erences in the ambient temperature.

It should be explained with reference to compensation for variations in line voltage (Fig. 2), that such errors as occur are due to the change which necessarily takes place in the resistance of 7, under what is referredto as cold conditions, with changeof line voltage. By theterm cold condition, is meant a state of afiairs in which resistance 12 is in circuit, and-only a small current flows in the resistances Sand 7, and in the relay 1. It is found that the ratio of the two small currents flowing in 6 and 7 under cold condition are appreciably altered by small changes in the line voltage, but that by the duplicate circuits employed in Fig. 3, this eifect which occurs accordingly in duplicate, may be eliminated or balanced out With regard to ambient temperature, it

is found in practice that by arranging resistances 7 and 7 -in such physical form that they may operate over a range of many hundred degrees centigrade, any error due to ambient temperature cannot be appreciated, but the compensating feature is present and may be utilized if the operating range be less.

Figs. 4, 5, 6 and 7 show arrangements for providing similar characteristics to Figs. 2 and 3 in slightly different manners. The circuit shown in Fig. 4, which is a counterpart of Fig. 2, employs exactly the same cycle of operations, but employs two resistances 7 and two resistances 6, and is arranged to give operation with a relay 1 provided with only one winding. This arrangement, however is not compensated for voltage. If, however, the connections shown on Fig. 5 be employed,,it is possible, utiliz- -In this latter case 1t should be noted that resistances 20 are employed which erform a function analogous both to that of resistances 6 and resistances 12, one of the resistances 7 and its corresponding resistance 20 operate always under cold conditions, and the presence of these latter is purely in the interest of compensation, as described. The other resistance 7 is caused to become heated when its corresponding resistance 20 is short circuited in a similar manner to short circuited in Fig. 2. With the latter resistance in circuit, however, acomplete in fact fol ow.

the efi'ect occurring when resistance 12 is balance bridge arrangement is arrived at. It should be noted with regard to the schemes employed in Figs. 4 and 5, that the resistance of the relay windings should have such relation to the resistances 6, 7, 20, etc.,

as to give the most efficient operation if the circuit be considered as a form of Wheat stone brid e, the principle of which it does The resistance, therefore, of the winding 49 should be large with regardto 7 and 20. This winding may be regarded purely as the resistance measuring coil, performing the same function as the single winding shown in Fi 4..

The additional winding 50' is provided forthe followingreason. In the absence of 5O itwill be-observed that the winding 49 becomes excited due to unbalance. immediately the resistance 20 is shortcircuited. It is required, however, and arranged for in previous diagrams that'there should be a definite heating period, this being controlled as explained by the temperature of 7.

The 'winding 50, therefore, during the heating period is arranged to provide ampere turns equal to and opposite to the ex citation provided in 49 when 20 is short.

circuited and when no heating of 7 has yet taken place. This counter-excitation,-'however decreases as heating. of 7 occurs, and the Operation of the relay, therefore, as hererelay operates when 49 preponderates to the necessary extent.

I tofore at'a predetermined tempera- Following operation of the relay --1 and relay 15, however, the coil is no longer I Y energized. and the relay functions as a reperiod as in previous arrangements.

- erred form of the invention for a definite.

' latter, however,

9 r asp a measuring device during the cool- The above .diagram constitutes the pretime'lag relay.

f Fi 6 shows an alternative arrangement,

capa le' of even greater precision, with,

which object in view abalanced beam type. of relay may be employed in place of a -;plain attracted armature.

-ment' is caaable of even more accurate re-- ose previously described, which are ingeneral preferable sults than In this connection it should be noted that the function'of relay 15 operating in conjunction with resistances 16, 17, etc.', is precisely as previously'described. In this case,

however, relay l is provided with a balance beam 21, fixed cores 22 and 23 and windings 24, 25 and 26-, the eflfect of cooling of this arrangement causing, as heretofore, decrease of the current in 6, and increase of the current in 7. This will cause the pull due to coil 26 to decrease with regard to the I voltage has been previously described, and

the eifect of winding 25 is to introduce an eflect, most easily determined by experiments, having re ard to the thermal characteristics of '7, which is arranged to be equal. and opposite to the discrepant efiect.

The extent of the compensation which .can

be obtained by this and the other methods described, is of the order which ,makes it possible to satisfactorily operate such a relay with an error not exceeding- 5% with a change in voltageof or 20%. It is of course understood-that theperfection of the I compensation depends to alarge extent on the precision of the-relays and apparatus involved, but the abovefigures may be taken to be commercial results. I y

In the foregoing; diagrams I have described various jinethods of carrying into effect definite time lag action in which a circuit may be closed or-by a difl'erent arrangement opened'at'a predetermined interval after a. controlling switch 8 is actuated. According to another, modification I show in Fig. 7 an arrangement such as isv fre-' .quently met with in protective devices and" control diagrams in which the timelag is of the control switchB. y

In Fig. 7, I employ resistances 7 and 20,

grams. It will be noticed that relay 1 has .now the armature 2 and'core 3, as before,

but has only one winding 4 and one contact closedwhenl: is energized. The operation will now be' as follows:

On'closing switch 8 relay 1 will, operate instantly dueto. the factithat one ofthe resistances 20 is short circuited, and them is initial out of balance current flowing'in through the terminals 10 and 11.

arranged to occur subsequent to the opening I 1 18 and relay 1,- otherwlse as in previous dia- .its winding, and will complete the circuit I In this case, as distinct "from the case shown in Fig. 5, .what isydescribed as the.

h at g c rrent a r ged to be arr ed continuously. Switch 8, therefore, will be closed for an indefinite period, but resist: ance 7 will, abrief interval after-the closing of 8, have attained a final steady temperature, and this will be maintained so long as switch 8 is closed. Immediately, however, switch'8 is opened 'the heavy current sufficient 'to maintain 7 at its hot temperature, ceases, and 'there flows instead what has been previously described as themea'suring current. Due to the' lack of balance between thev hot resistance 7 and the cold resistance, 7 however, relay 1 will not open immediately 8 is opened butwill continue to energize 10 and 11 until such time as the two resistances 7 are sufficiently in balance to allow the. armature 2' to open the contactwhen the relay operating circuit is completely opened, at the same time energy being out off from 10 and 11. It is tobe noted that this arrangement is compensated as described with regard to Fig. 5, both for variations in operating voltage and for change in ambient temperature should this be comparable with the operating tempera- 'ture of the hot resistance 7.

In Fig. 8 we show the application of this thermal principle to a relay such as is commonly describedas a notching relay, this being the term given to the form of relay.

which is frequently employed in connection with auto-reclosing apparatus, and having the following characteristics:

The relay is arranged to close or open its circuit as may be required, not when the relay is energized, but only after the relay has been energized and the circuit brokena given number of times in succession within a given interval. To achieve this, it is common to employ a time lag element and -a notching mechanism such that the contacts can only be operated when a given number of notches have been effected. The time lag element is introduced on the relay being vdeenergized, so that the relay in eflect has a time lag reset characteristic which is arranged to release a latch on the notching mechanism 'a given time after the relay mature 32, which is pivoted on 33, and arranged to be attracted by core 34 when coil 28 is energized to the necessary extent.

r Armature 32 is restrained by spring 44, the contacts 30 and 31 being normally openedtherefore unless coil 28 is energized. The main contact 35, which when bridging contacts 36 closes a circuit between terminals 10 and 11, attached to a spindle 37 on which is mounted a ratchet wheel 38. In

this instance the contacts 35 and.36 are arranged to close an entirely. separatecircuit ratchet wheel 38.

Lever 39 is constructed of such a shape as to form a latch engaging on the teeth of wheel 38, when it is permitted to do so by the projection 45 on the lever 32, which is arranged so that this only occurs when coil 28 is energized.

When coil 28 is deenergized, the relative strength of springs 43 and 44 are so arranged that latch 39 releases wheel 38; Thus the releasing value for 32 is independent of friction between latch and tooth. I

The lever 40 pivoted at 42, is made integral with the armature 46 which is attracted by the core 51 when excited by coil 29, and is provided with a pivoted catch 48 arranged to engage with the teeth of the wheel 38, so that when 29 is energized, wheel 38 moves through one tooth pitch. On coil 29 being deenergized, wheel 38 is constrained by a spring not shown, to return to its original position unless coil 28 is energized, in which case it will be retained in the position which it has assumed due to the movement of lever 40. Movement of armature 46 to the attracted position is resisted by spring 47.

The operation of the complete arrangement is as follows: On the closing of switch 8, winding 29 becomes energized, attracting 46 and causing heating of one of the resistacnces 7 followed by the energization of winding 28, causing operation of armature 32 and lever 39, due iZO the unbalancing effect. If switch 8 is now opened, lever 40 will recede, but lever 39 will continue to engage with a tooth on-wheel 38. Assuming that switch 8 is not reclosed, one of the resistances 7 (the hot one) slowly cooling, will cause the circuit comprised by the cir .cuit resistances 7 and 20-to become more and more balanced, causing in consequence the current in 28 to be correspondingly reduced.- In due course, therefore, 28 will no longer retain the armature 32 causing the I are pivoted respectively at '41 and 42 the former being constrained by spring 43, to move towards the contacts 30 and 31 to open, at the same time v constraining lever 39 to release 38. If on the other hand, switch 8 had been closed a second time before the release of 38 after the manner described, a second operation of 40 would have occurred, causinganother tooth of 38 to be engaged. I

It will be seen therefore that in accordance with the setting of the notching mechanism, a number of consecutive operations of I switch 8 will finally cause the contacts 36 to be closed by the bridge piece 35, provid ingthat there does not elapse after each openingof 8 an interval of time greater than.

.to the magnitude 0 a current, over oad, etc,

and in Fi 8 I show after what manner this may be ac ieved. In this case it is assumed that a source of operating energy is avail-1 able for operating the mechanism of the re-Q I lay distinct from the current according'to the magnitude of which'I wish to control the time lag. A

In Fig. 9 I employ resistances 7, 16, 17,

20, etc., as in Fig. 5, and relays 1 and 15.

Relay 1 is provided with wind ngs' l and ,5. having functions precisely as specified hereinbefore. Relay 15 is also rovided with a winding exactly as describe in Fig. 5; Relay 15, however, is provided with an additional stationary contact 52 and a movable contact 53, mechanically coupled to or mounted on its armature, and arranged to open circuit when relay 15 is operated.

relay 1 is now pivoted. centrally, but has the same contacts as in'the The armature 2 of previous diagrams. The magnetizing effect due to 1 and 5 is arranged to provide exactly the same operation as in Fig. 2 and onwards. In Fig. 9, however,xcontacts of Fig. 1 will be shown upside down as cornopposite side of the fulcrum'on which the armature 2 pivots, we provide an additional core 54 excited by a winding 55; To the right of the diagram I show three con'du c,

tors 56 representing for the sake of example,

a three-phase circuit. On one of these con-l 'ductors I show a current transformer 57 whose secondary is arranged to excite the winding 55.

Core 54, therefore, will attract the armature 2, with a force depending on the strength of the current flowing in the three- .phase circuit 56. It isto be noted that the spring or other restraining effect which though'not shown is understood to control 2, is arranged to constrain 2, to assume the position shown on the diagram, and it will beseen that the effect of core 54 is to assist such action. If, therefore, the whole diagram be considered tooperate as a definite time lag relay,, entirely as described with regard to diagram 5, it will be recalled that.

during the cooling period the contact on the end of 2 will be closed on the upper fixed contact and during this period, the force due to the restraint of 4 and 5, will be slowly decreasing .When this resultant forcehno longer exceeds the resetting efiortfof the spring or controlling means, the armature moves downwards closing on' to its bottom contact, and-'xcompleting the circuit i010 and 11. It will be'iclearly comprehended, there.

"fet that if the effect or coil'55 is'to assist-the controlling means, it. will due to this fact, shorten the periodot time lag, and by suitably designing the winding 55, the actual duration ot-*thetime lag'may be made in-- .verselyfproportional to the strength of the in Jorderto-stop the heating when the resistance? has attained-a, certain temperature. For this "therefore, I have" shown the contacts 53 and52 mounted "on the relay "15, which are arranged to short circuit the current transformer 57 during the heating -period, only energizing the coil 55 on the ,cominencementofthecooling period. It is t'o'be noted, therefore, that even should the currentin thelo'ad circuit 56 be excessively higngaueto a severe short circuit, the armature 2 will carryout its normal heating cycle, which in practice would be of the order of a .fraction of a second, and that immed ately on the operation of .relay 15 it would due to the very high excitation of 1coil immediately return to the bottom pared with previous diagrams, for the sake of convenience, as the extremity of arman, ture 2 is now moving in the opposite direction when attracted by the core 3. 'On the;

contact -This fives; the arrangement the characteristic o a. definite minimum time lag sinceno matterhow heavy may be the cur-rent in theload circuit, the heating cycle ymust, he] carried out following by instanta- {neoue'operatmn of the relay 15 and the return. movement of contact 2.

: With regard to the resistances 7 referred to throughout the specification, Ihave found consecutive operations being made. It has been noted in the case of gas-filled bulbs that after three or four operations a slight error is introduced which is due to the heating of the gas surrounding the tungsten wire.

It is not essential that the resistance which "'EXFBllGIlt results for time. lags up" to half- -minute to be given by tungsten wires varies with the temperature should have a positive temperature coefficient as materials such as boron withva negative temperature coefficient may also be used with correspondmg modification of the balancing clrcults. I- prefer however to use the positive, temperature coeflicient of a metal such as tungsten because this metal is readily obtainable in the form of wire with, the same characteristic properties in diiierent batches. liloreoverits high melting point permits of a wide range of temperature variation being used.

The tungsten resistance enclosed in an evacuated bulb may be operated at'a temperature such that the life of the device. will be much beyond the thousand hours average aimed at in lamp manufacture. In order to slow down the rate of cooling the resistance may.

be shrouded by a cup or other suitable form of heat'storage arrangement.

What I claim as new and desire to secure byLetters- Patent of the United States, is,

time'interval after said means is subjectedto a difierent temperature condition, and switch mechanism and connections whereby the circuit controlled by the device is energized only after the said controlling member has performed each of its two 1nove-- ments. I

2. Atime element cincult controlling device comprising amovable controlling member capable of two movements, thermal responsive means for giving the controlling member one of its two movements a time. interval after the thermal means is subjected to a predetermined heating effect and v for giving the controlling member the other of its two movementsa time interval after a predetermined reduction in the heating of said thermal means, means controlled by said controlling memberand cooperating -with said thermal means for reducing the heating thereof, and switcli mechanism and connections whereby the circuit controlled by the device is energized only after the said controlling member has performed each of its two movements.

. 8'. A time element circuit controlling device comprising thermal responsive means having a controlling member operable betweentwo positions'responsively to predetermined variations in the temperature of said means, means for ele'ctrically'heating said thermal responsive means to operate said member from the first of said positions to the second of said positions, means cogntrolled by said member for controlling the said electrical heating means to effect the return of said controlling member to the first position, and switch mechanism and connections whereby the circuit controlled by the device is energized only after the said controlling member has been operated to said second 'position and returned to said first position. 3

4( A time element circuit controlling dcvice comprising thermal responsive means having a circuit controlling member operable to one position when the temperature of said means is at one value and to a. second position when the temperature of said means is at another value, electroresponsive means controlledby said member in said second-position and cooperating with said thermal responsive means for controlling the heating thereof to return said member to saidone position, .and connections where-i by the said circuit controlling member is required to move to said second position and then return to said oneposition under the control of said electrorcsponsive means prior to energization of the circuit controlled by the device, 0

' 5. A time element circuit controlling device comprising thermal responsive means having a circuit controlling member operable with a time delay to and from a circuit tions in the temperature of said means, an auxiliary switch cooperating with said member to jointly control a. circuit, means whereby said auxiliary switch is operated to control the circuit, a. time'interval after the operation of said member-from said circuit controlling position, and means for controlling the temperature of said thermal responsive means to return said member to said circuit controlling position a time interval after the operation of said auxiliary switch. i

6. A time element circuit controlling device comprising thermal current responsive means having a circuit controlling member operable with a time delay to and from a circuit closing position responsively to predetermined variations in the energizing current thereof, an auxiliary switch connected in series with said member to jointly control a circuit, means whereby said switch is 9 closed a time interval after the operation of said member'from said circuit closing position, andconneotions for controlling'the energiz'ing current of said thermal responsive means to return said member to said circuit closing position a time interval after the closure of said auxiliary switch; a

'7. A time element circuit controlling device comprising electrically heated thermal responsive means having a circuit controlling member operable from a circuit controlling position to another position responcontrolling position -responsively tii 'varia sively to a predetermined heating effect, an

electroresponsive switch cooperating with said member to jointly control a circu t,'and connections whereby said electroresponsive switch is operated to the circuit controlling position upon the operation of said member to said other position and the heating of said thermal responsive means is controlled to return said member tot-he circuit controlling position a time interval after the operation of said switch.

8. A time element circuit controlling device comprising a movable switch member decreased upon the operation of said electromagnetic switch to said circuit closing position to permit said movable switch member to return to the circuit closing position, and

connections whereby the circuit controlled by the device is energized only when said switch member and said electromagnetic switch are in their respective circuit closing positions.

9. A time element thermal responsive dea vice comprising a pair of circuit controlling members each operable between two positions and biased toone of said positions, electrically heated thermal responsive means for operating the first of said members from the biased position to itsother position re- .sponsively to the heating effect of a predetermined current, electroresponsive means controlled by said first member in said other position for operating said second member from the biased position to its other position and for maintaining the same therein, and means controlled by said second member for reducing the heating current of said thermal responsive means to permit said first 'member to return to the biased position a time interval after the operation of said second member to its other position, and con nections whereby the circuit controlled by the device is energized when the first of said ond of said members is in its other position.

10. The combination in a time element switch of a switchmember, electroresponsive means for controlling the said switch member, a resistor having an appreciable temperature coefficient, a multiple connected resistor having a materiall lower temperature coefficient, the said resistors connected in a circuit to be heated responsively to the current therein and arranged to control the said electroresponsive means responsively to the diflerence in the resistance of the said resistors due to heating thereof, auxiliary switch mechanism controlled by the said switch member, and a resistor in the circuit of the said multiple connected resistors under the control of the said "auxiliary switch mechanism for controlling the heating on said multiple connected resistors.

11. A time element switch as specified in claim 10, characterized by the fact that an additional set of multiple connected difierent thermal coeflicient resistors are provided and connected in multiple relation with the multiple connected resistors specified in claim 10, so as to compensate for changes in ambient temperature and operating current or potential.

In witness whereof, I have hereunto set 86 my hand this seventh day of May, 1923.

ALAN STEWART rrrz GERALD.

members is in its biased position and the sec- 

